Borneo tourism can be categorised as follows
Sabah, Malaysia : Coastal resorts and mountain climbing with diving at Sipidan (MH fm BKI), islands not more than 30 minute boat ride for a few dollars. NorthEast Sabah neighbouring islands are Southern Phillipines, known for its pirates and tourism detentions.
Brunei : Not much here, good road connections to local towns/villages. No alcohol in country so tends to put tourists off. Generally only a staging point to either Sabah or Sarawak if you choose this route.
Sarawak : Throughout MH offer hopping schedules but only coastal sites as Indonesia borders close by. Kuching tends to be stop off for jungle trekking and Iban river boats, again very cheap.
Tourism hotels on the coast.
Balikpapan, Indonesia.: Recent tribal conflicts don't attract tourism, very sparse population. I think only Garuda serve BPN now from Indo mainland.
Having traversed several rivers in both Sabah and Sarawak in a boat, I certainly wouldn't want to try landing on one. Boat repairs were very costly when we came across some sunken trees and logging. Generally the river depth inland is extremely shallow, 6-12 inches and full of rapids and overhanging obstructions so this would preclude floatplane ops.
Another point against F/plane ops would be the massive contingent of little ''suicide boats'' flying about the city centre rivers and harbours. I refer to them kindly due to their carefree way of driving at great speeds without due concern. Dont expect them to look up for a landing f/plane or to give way after all its their trade you'll be taking away.
If your post is to sound out the feasabilty to start operations, then good luck but don't count on Government support, it doesn't exist here unless there is something in it for them.